Updated 16 October 2015

Urinary tract infection

A urinary tract infection is an infection involving part or all of the urinary tract.

Summary

25-30% of women between the age of 20 and 40 years have had urinary tract infections

80% of urinary tract infections are caused by the bacterium E.coli

40% of patients with a urinary tract infection have a recurrence within one year

All men and children with even one urinary tract infection, and women with recurrent infections, should be investigated for underlying causes

Obstruction plus infection is a true medical emergency

The vast majority of urinary tract infections can be treated successfully with antibiotics

Complications are not common, but can be serious or even fatal

Description

A urinary tract infection is an infection involving part or all of the urinary tract. The effects of the infection depend on the interaction between the bacterium and the host’s defence mechanisms.

If the brunt of the infection is situated in the bladder, the symptoms tend to be of a local nature and the disease is called cystitis, or a lower urinary tract infection. Infection involving mainly the kidney is called pyelonephritis, or an upper urinary tract infection. In pyelonephritis the symptoms tend to be of a more systemic nature, such as fever, chills and a fast heart rate.

The division between upper and lower urinary tract infection is somewhat arbitrary, since the infection enters the system by an ascending route via the urethra (the tube connecting the bladder to the outside) in both cases. The bacterium E coli is responsible for 80% of urinary tract infections.

TB of the urinary tract, kidney abscess and infections of the male genital organs (prostate, testicles and epididymis) are dealt with in related topics (see below). Infections of the female genital tract are not regarded as urinary tract infections.

Cause

A urinary tract infection is the result of an interaction between the bacterium and the host (patient). Virulent (aggressive) bacteria are able to overcome normal host defence mechanisms. Less virulent bacteria can lead to significant infections in patients with abnormal urinary tracts or compromised immunity.

Most bacteria reach the urinary tract via the ascending route, traversing the urethra, bladder and sometimes the ureters up to the kidneys. The main source of these bacteria is the patient’s own large intestine. The female urethra is short and situated close to the faecal reservoir, explaining the much higher incidence of urinary tract infections in females compared to males.

Escherichia (E.coli) is responsible for 85% of community acquired and 50% of hospital acquired urinary tract infections. Other organisms include Klebsiella, Proteus, E faecalis and Staphylococcus saprophyticus.

In diabetics and immuno-compromised patients, fungi such as candida and viruses (adenovirus, cytomegalovirus) account for a significant percentage of urinary tract infections. Certain special organisms reach the kidneys via the bloodstream rather than the ascending route. These include Mycobacterium tuberculosis, which causes TB, and Staphylococcus aureus, which can cause a renal abscess.

Symptoms

Upper Urinary Tract Infection (pyelonephritis)

Fever: usually above 38 degrees

Chills and shakes

Vomiting

Pain in the loin, which is the area in the back between the lowest (12th) rib and the hipbone

Pyelonephritis is usually unilateral, affecting only one kidney. Bilateral involvement is less common, but not impossible. Despite the presumed ascending route of infection via the urethra, bladder and ureter to the kidney, bladder symptoms are usually non-existent or mild.

Lower Urinary Tract Infections (cystitis)

Frequency: the frequent passage of small amounts of urine

Urgency: a great desire to urinate, with difficulty postponing urination (urgency is usually associated with frequency)

Dysuria: pain and burning while passing urine

Haematuria: blood in the urine

Suprapubic pain: pain over the bladder area - the lower part of the abdomen above the pubic area

Patients with cystitis have severe local (bladder) symptoms, but tend not to be systemically unwell. Fever, rigors and a fast heart rate as seen with pyelonephritis are usually absent. Note that blood in the urine can be caused by other more sinister causes than cystitis, such as bladder cancer. Blood in the urine should not be assumed to be due to cystitis unless other more serious causes have been excluded.

Prevalence

The exact incidence of urinary tract infections in South Africa is not known. With the exception of the newborn period urinary tract infections are much more common in women than in men. In the USA urinary tract infections necessitate or complicate over one million hospital admissions annually.

Surveys screening for bacteriuria (bacteria in the urine) have shown that 1% of schoolgirls aged 5-14 years have bacteriuria and that this figure increases to 4% by young adulthood and then by an additional 1-2% per decade of age. The prevalence of urinary tract infections in young women is 30 times that of young men. However, with increasing age this ratio decreases as relatively more older men develop urinary tract infections. This is probably related to the high incidence of prostatic enlargement in older men, which leads to urinary stasis and an increased risk of infection. 25-30% of women between the ages of 20 and 40 years have had urinary tract infections. 20% of women and 10% of men over 65 years of age have bacteria in the urine. The prevalence of bacteriuria also increases with institutionalisation or hospitalisation and concurrent disease such as diabetes. About 40% of patients with urinary tract infections have a recurrence within one year.

Course

The course of a urinary tract infection will depend on a number of variables, including:

the status of the infected urinary tract

the immune status of the patient

the virulence of the organism

the effectiveness or not of treatment that has been initiated.

Uncomplicated cystitis in a patient with a normal urinary tract and an uncompromised immune system usually resolves with or without treatment. The initial symptoms of urgency, burning with passing urine, and lower abdominal pain usually only last for a few days. The standard treatment of a short course of broad-spectrum antibiotics accelerates the clearance of infection. Otherwise healthy patients can expect to be symptom-free after 2-3 days. Follow up urine cultures should be sterile.

In patients with abnormal urinary tracts (e.g. catheters, stones, bladder outflow obstruction) or compromised immune systems, infection can be difficult or impossible to clear. These patients often need longer than standard courses of antibiotics. If the underlying abnormality can be corrected this should form part of the treatment. Patients with abnormal urinary tracts are also more likely to develop complications (see below).

Anybody who has had one infection is more likely to develop subsequent infections. About 40% of patients with one urinary tract infection have a recurrence within one year. Recurrent infections can be caused by the same or a different organism (bacterium). Whether the initial infection was treated or not does not seem to alter the incidence of recurrent infection. Long-term prophylactic antibiotic treatment reduces the rate of reinfection during the treatment, but does not alter the patient’s basic susceptibility to infections. After the antibiotic prophylaxis is stopped, the rate of infection returns to the pretreatment rate.

Patients can expect to see a response after two to three days of treatment. The heart rate and temperature should return to normal and the patient should feel better. If an appropriate response is not seen despite a suitable antibiotic, patients should be investigated for an underlying abnormality or complication (e.g. stone, obstruction or abscess). Patients with underlying abnormalities or compromised immunity are more likely to develop complications.

Risk factors

Risk factors can either be general, usually affecting the immune system, or local, in which case normal emptying of the bladder is impaired.

General factors

Extremes of age: infants and old people have less resistance to infection

Diabetes, which increases the risk for urinary tract infections in several ways:

glucose in the urine is an excellent culture medium for organisms

diabetes impairs the immune system by hampering the function of white blood cells that are vital in the fight against infection

diabetes can also damage the nerves to the bladder, causing a floppy poorly contracting bladder, leading to urinary stasis

Any cause of impaired immunity:

malnutrition

HIV/AIDS

cancer

chemotherapy

immunosuppression

diabetes

Local factors

The body’s main protective device against urinary tract infections is the regular complete emptying of the bladder during voiding. Even though bacteria may get into the bladder, they are usually washed out before a significant infection can develop. The tubes (ureters), which drain urine from the kidneys to the bladder, have a one-way valve at their lower end where they enter the bladder. Any condition that impairs the normal flow of urine, or interferes with normal emptying, will predispose to infection.

Risk factors are:

Obstruction of the upper tracts (kidneys and ureters) due to:

stones

pelviureteric junction obstruction: congenital obstruction at the upper end of the ureter

Vesico-ureteric reflux: this is failure of the normal one-way valve mechanism where the ureter joins the bladder, causing urine from the bladder to go back up to the kidneys during voiding

Foreign bodies in the urinary tract, including:

urinary catheters

ureteric stents (long term internal drainage tubes)

urethral stents (long term internal drainage tubes)

nephrostomy tubes (external drainage tube draining the kidney)

Fistulae. These are abnormal connections between different organs. Fistulae between the bladder and vagina, or between the bladder and colon, lead to urinary tract infections, which are impossible to eradicate with antibiotics alone.

Instrumentation of the urinary tract as a result of:

prostate biopsy

cystoscopy (looking into the bladder with a special endoscope)

surgery such as transurethral resection of the prostate gland

Trauma to the urinary tract, for example in the case of a stabbing

When to see a doctor

Not all self-diagnosed urinary tract infections turn out to be urinary tract infections after all. Some sinister and other less serious conditions can masquerade as urinary tract infections.

The role of the health professional includes making an accurate diagnosis, treating the acute event and investigating patients for underlying predisposing factors.

The following patients with a suspected urinary tract infection should see a doctor urgently:

All children

All cases of suspected pyelonephritis

All cases with blood in the urine

Anybody known to have only one kidney

Previous history of stones

Previous history of surgery to the kidneys

Anybody with a high fever

Vomiting

Severe pain

Anybody with pain in the right lower abdomen who still has an appendix

All pregnant females

No response to antibiotics after 2 to 3 days of treatment

Following the (successful) treatment of the acute event, the following patients should be investigated for possible underlying predisposing causes:

All children

All males

All cases of pyelonephritis

Females with more than one attack of cystitis

Everybody with blood in the urine (at any stage)

Anybody with a urinary tract infection which seems difficult to eradicate with standard antibiotics

Diagnosis

The diagnosis is made by means of a history, physical examination and special investigation of the upper and/or lower urinary tract infection.

Upper Urinary Tract Infections (pyelonephritis)

The diagnosis is made by means of a history, physical examination and special investigations (tests).

History: see symptoms

Clinical examination:

high temperature, often above 38.5 degrees

fast heart rate

tenderness over the kidney

Tests:

Urine microscopy: urine is investigated under a microscope for evidence of white blood cells, red blood cells and organisms. The offending organisms can usually be cultured from a urine and/or blood culture. If an organism is grown in culture it can be tested for sensitivity against various antibiotics to ensure effective treatment.

Blood count: a full blood count will show a raised white cell count, which indicates infection.

Imaging: the urinary tract is imaged by either ultrasound scan or intravenous urography (IVU or IVP). An ultrasound machine uses sound waves to create an image of underlying structures. An intravenous urogram involves injecting an iodine based contrast material into a vein. The contrast is excreted by the kidneys and is visible on plain X-ray. A series of films is taken after injection of contrast to show up the kidneys, ureters and bladder. Both ultrasound and IVU will show up common problems like kidney stones or obstruction of the urinary tract. If there is a suspicion with the initial presentation that the underlying infected kidney may be abnormal, the imaging (ultrasound or IVU) is performed straight away. However, in a straightforward case of pyelonephritis, in which the patient responds promptly and completely to antibiotics, the tests can be done at a later date once the infection has cleared up.

In children with urinary tract infections the incidence of underlying abnormalities is high. An obstructive lesion will be found in 4-10% and reflux in 30-50% of children with proven urinary tract infections. An ultrasound scan is usually the method of choice to rule out an obstructive lesion, which is the more serious of the two possibilities. Once the infection has been treated a micturating cystogram is performed to demonstrate or rule out reflux. In this latter test a contrast material is instilled into the bladder via a small catheter. X-rays are then taken while the child passes urine to see if bladder contents (contrast) pass up the ureter(s) into the kidneys.

In children the combination of reflux and infection can lead to kidney scars. The presence or absence of kidney scars often determines the management of the underlying reflux. Scars are demonstrated with radioisotope scans. In these tests a radioisotope is injected into the body. The radioisotope is linked to a substance which is excreted or absorbed by the kidney. A special gamma camera, which measures radioactivity, is then used to measure the activity over the urinary tracts. In this way kidney scars can be diagnosed accurately.

Lower Urinary Tract Infection (cystitis)

The diagnosis is made by means of a history, physical examination and special investigations (tests).

History: see symptoms

Physical examination: tenderness over the bladder is often the only positive clinical finding. Patients with cystitis are usually not very ill. The temperature is usually normal.

Tests:

Urine samples: show red blood cells, white blood cells and organisms. The offending organisms can be cultured and identified from the urine.

Blood tests: in simple cystitis it is not routine to do extensive blood tests

Imaging: in women with isolated cases of cystitis no imaging is required. In men, bladder outflow obstruction (enlarged prostrate or urethral stricture) needs to be ruled out. This can be done by ultrasound scan and cystoscopy (looking into the bladder with a special telescope).

Children need to be investigated fully, as in pyelonephritis (see above). Ultrasound scan and micturating cystogram will demonstrate most underlying abnormalities.

Treatment

Home

Mild to moderate uncomplicated cystitis will probably resolve with or without treatment. Conservative measures include increased oral intake of fluids and agents to alkalinise the urine (e.g. Citrosoda). Antibiotics expedite recovery.

Upper urinary tract infections and pyelonephritis are not suitable for home treatment. Some patients with recurrent urinary tract infections are issued with antibiotics, which they take as soon as symptoms develop. They are usually expected to take a urine sample prior to commencement of treatment.

Medication

A few organisms cause the vast majority of urinary tract infections. E coli account for 80% and staphylococcus saprophyticus for 5-15% of infections. Other less commonly involved organisms include Klebsiella, Proteus species and Enterococci. A urine sample is taken prior to commencement of an antibiotic, which can be expected to cover the above organisms. Should the culture and sensitivity results deem otherwise, the antibiotic can be changed as is appropriate. The most commonly used drugs are co-amoxiclav (Augmentin), the cephalosporins and fluoroquinolones. In South Africa there is a high level of bacterial resistance against amoxicillin, ampicillin and trimethoprim-sulphamethoxazole (Bactrim).

Commonly used treatment regimes:

Uncomplicated cystitis in women: a three-day course of oral antibiotics is most effective. Single dosage regimes can be effective, but have a high relapse rate. Longer courses of treatment are no better at eradicating infection than 3-day courses, and lead to a higher incidence of treatment-related complications. Longer courses cause a greater disturbance in the patient’s own natural flora and are more costly.

Uncomplicated cystitis in men: a 7-day course is standard treatment.

Uncomplicated upper urinary tract infection (pyelonephritis): severe cases are admitted to hospital and treated with intravenous fluids and antibiotics for one to two days, and thereafter with oral antibiotics (for 10-14 days) once the temperature settles. Less severe cases are treated with oral antibiotics for 10-14 days.

Surgery

Surgery has no primary role in the treatment of urinary tract infections. Some of the complications of infections are treated by surgery, such as the drainage of kidney abscesses. Some of the underlying abnormalities that predispose a patient to infection can be corrected surgically, such as the removal of stones or the alleviation of obstruction.

Prevention

Adequate fluid intake to ensure the passage of 1½-2 litres of urine per day. There is no benefit in excessive fluid intake.

Women should always wipe from front to back after passing stool.

Women should empty the bladder after sexual intercourse.

Avoid spermicidal creams and diaphragm contraceptives as both these are associated with a higher incidence of urinary tract infections.

Regular intake of cranberry juice appears to have a protective effect. A substance in cranberries prevents the adhesion of bacteria to the lining of the urinary tract.

Daily low dose prophylactic antibiotics reduce the rate of infection in patients suffering from recurrent infections. However, this does not alter the underlying propensity to develop infections once the prophylaxis is stopped.

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